Method of refining oil



United States Patent METHGD 3F REi iNENG (Bill.

Robert H. Campbell, il'rexei Hill, and Irwin H. .iohnson,

Chester, Pa, assignors to Sun Oil Company, Philadelphia, Pa., a corporation of New Eersey No Drawing. Filed Sept. '7, 19b2, er. No. 222,225 11 Claims. (Cl. ass-are This invention relates to the treatment of lubricating oils that boil generally in the lubricating oil range in order to improve their qualities for various uses. Oils treated according to the invention have high oxidation stability and low percent power factor and hence are particularly suitable for use in electrical applications such as transformer oils, refrigerator oils, cable o'ds, and the like.

In the use of oils in electrical applications such as, for example, transformer service, it is important that the oil have a high resistance to oxidation, especially in the presence of metals such as copper and iron. In addition, it is important that the oil have a low percent power factor in order to reduce power losses to a minimum. Therefore, a method of treating oils to produce an oil of high oxidation resistance and low percent power factor would be desirable.

Commercial electrical oils are customarily tested for oxidation resistance by a test procedure developed by the Doble Engineering Company of Belmont, Massachusetts. The test procedure is described in ASTM Standards on Electrical Insulating Liquids and Gases, pages 307-313, December 1959. The procedure involves bubbling air through a known amount of the oil held at a temperature of 95 C. in the presence of copper and iron, and making two tests daily on small samples of the oil. One type of test is an acidity measurement. The second test is a precipitation test in which one volume of the oil is diluted with five volumes of pentane, the mixture is allowed to stand at least eight hours, and the presence or absence of a sludge precipitate is noted. The endpoint of the Doble test is taken as the number of days of oxidation either before the acidity of the oil reaches 0.25 mg. of KOH per gm. of oil or before a positive pre cipitation test for sludge is obtained.

Another test which further defines the suitability of the oil for transformer service is the percent power factor test. During the Doble test procedure described above, the percent power factor of the oil is periodically measured.

To be commercially acceptable for transformer use an oil should have a life of three days or more under Doble test conditions. In addition, the power factor at the end of three days should be l-2%. Oils treated according to the present invention meet both of these requirements.

A conventional refining procedure for the preparation of transformer and other electrical oils involves a preliminary solvent extraction such as extraction with furfural, treatment of the resulting rafiinate with concentrated sulfuric acid typically in amount of 20 lbs. per barrel, and then treatment with adsorptive clay typically in amount of 35 lbs. per barrel. However, with stocks derived from naphthenic crudes and having viscositygravity constants in the range of 0.84-0.92, this type of treatment generally produces an oil having a Doble test life of 2-3 days and a three-day percent power factor of 15-20%. Hence a more eifective type of treatment is needed. 0

It has now been found that mineral oils having a Doble test life of 3 days and a three-day power factor of 1-2% can be prepared by concurrently treating the oil with concentrated sulfuric acid, copper metal or an inorganic copper salt, and an inorganic ferric salt, followed by a subsequent treatment with adsorptive clay.

The invention is best described in the following manner:

The charge oil can, if desired, be subjected to a preliminary solvent extraction, such as extraction with furfural, but this is not necessary to the successful practice of the invention.

The charge oil is initially contacted concurrently with sulfuric acid, copper metal or an inorganic copper salt, and an inorganic ferric salt for a period of 20-35 minutes and at a temperature in the range of to 130 F., preferably F. The three treating agents must be employed concurrently. If any of the treating agents are omitted, the beneficial results of the invention are not obtained. 1

The sulfuric acid should be concentrated, i.e., 90-- l00%, and should be used in the amount of 15-30, preferably 20, lbs. per barrel (1 bbl.=42 gal.) of oil. The copper can be used, as mentioned above, either as copper metal or as an inorganic copper salt such as copper sulfate, copper oxide, and the like. The amount of copper metal or copper salt used should be at least 1.5%, preferably 1.83.0%-, as copper, based on the weight of the charge oil. Any inorganic ferric salt such as ferric chloride, ferric sulfate, and the like can be used but it is essential that the iron be used in the trivalent form. When bivalent iron salts such as-ferrous sulfate, ferrous nitrate, and the like are used, the finished oil has a substantially higher percent power factor than when trivalent iron salts are used. The amount of ferric salt used should be at least 0.4%, preferably 0.4-1.0%, as iron, based on the weight of the charge oil.

The three treating agents described above will be referred to collectively hereinafter as the acid, copper, and iron treating agents.

The initial contact of the oil with the acid, copper, and iron treating agents should be for a period of 20* to 35 minutes. It will be seen in the examples here inafter that the power factor of the finished oil reaches a minimum when the contact time is within this range but is substantially higher when the contact time is either below or above this specified range. The temperature at which the initial contact is carried out should be in the range of 90 to F., preferably about 110 F.

The initial contact of the oil can be effected in any desired manner. For example, the oil can be charged to a tank following which the acid, copper, and iron treating agents are added separately. Preferably the contents of the tank are agitated in order to insure efficient contact of the treating agents with the oil and with each other. Alternatively, the acid, copper, and iron treating agents may be admixed separately and the admixture then charged to the tank containing the oil. The temperature at which the initial contact is carried out is most conveniently maintained within the specified limits by equipping the mixing tank with heating coils, a heating jacket, etc.

When the acid, copper, and iron treating agents are added to the oil, essentially two liquid phases result. One is an acid phase, the other is an oil phase. In addition, some sludge usually forms by reaction of the treating agents with the oil. After the prescribed contact period of 20-35 minutes has elapsed, the agitation in the mixing tank should be shut off and the phases allowed to separate. The acid and sludge settle to the bottom of the tank, the oil phase remains on the surface and is then separated by, for example, decanting.

The separated oil layer can, if desired, "be water washed prior to clay finishing. Water washing is desirable in that it removes the last traces of acid from the oil, thereby reducing corrosion of equipment in subsequenthandling of the oil.

mixing the acid with the oil.

Doble life of 2 days'and a three-day power factor of The separated oil is next subjected to treatment with adsorpti-ve clay. Any conventional adsorptive clay such as fullers earth and the like can be used, and the clay treatment can be carried out in any conventional man- Thus the clay can be added to' a tank containing the oil, the mixture agitated, and the clay then separated nae-a. 7

. This shows that treating the'oil with sulfuric acid, copper,

' from the oil by filtration. Alternatively, the oil can be and a ferric salt does produce an oil having a Doble life of 3 daysand a power factor of 12%. I

. EXAMPLE VI and ferric sulfate was held at 110 F. for 45 minutes The following examples illustrate the invention more specifically i j EXAMPLE I 1 a The charge oil was a naphthenic distillate'stock suitable for electrical transformer use. The oil initially had the j following properties: A.'P.'I. g-ravity24.4; Flash Point=280j FqFir efPoint=3l0 FL; S.U.'S. Viscosity cosity-Gravity C-onstant =0.88, j

The above charge oil was first extracted withjfurfural at room temperature using only enough furfural to yield 95% raffinate.-. This raffinate' was then divided into eight portions identified as Oil 1, Oil 2, Oil 3 Oil 8: 'Oil 1 was mixed with .20 lbs. of sulfuricacid perbarrel of oil and held at-110 F. for rninutes. The oil was separated from the acid-by decanting, and the oil washed with water. The washed oil was next treated at 220 7 .F. with lbs. of adsorptive clay per barrel of oil. Finally the adsorptive clay was'separated from the oilby filtration. The finished oil had a Doblelife of 2 days and a three-day power factor of 18.1% These results show that merely treating the oil with sulfuric acid and clay does not produce a satisfactory electrical oil. 7 3

' EXAMPLE 11- Oil 2; was treated by the same'procedure as in'Example I except tha-t 2% copper metahbased on the weightof the oil, was-added to the sulfuric acid before mixing the acid with the oil. The finished oil'ha d a Doble life of 3 days and a three-day power factor of 5.0%. This shows thatwhile treating the oilwith only "sulfuric acid andcopper metal does produce an oil having a Doble life of 3 days, it does not produce an oil having a threeday power factor of 1 -2 I 7 p EXAMPLE III 2 Oil 3 was treated by the same procedureas in Example 1 except that 2% ferric sulfate (0.56% iron), based 7.0%. This shows that treating the oil with only sulfuric acid'a'nd aferric salt does not produce an oil having. f

athree-day Doble life and a' three-day power factor of 72%?" i EXA PLEI y w Oil 4 was treated by the same procedure as inExai-rk 'ple 1 except that 2% copper metal; based. on. the weight wof oil; and 2.08% ferrous sulfate (0.56% iron), based on the weight of :oil was addedto the sulfuric acid be- 'over, treatment with sulfuric acid and copper alone."

7 n 2 EXAMPLE V V Oil 5 was treated by the-same procedure as in Example IV except that 2% ferric sulfate (0.56% ir on) w as used instead of ferrous sulfate. The finished oilhad a' Doble "life. of 3 days and a three-day power -fact0r=of=1.5%.

The finished oil hada' on weight ofoil, was added to the sulfuric acid before,

instead of 30' minutes. The finished oil had a Doble life of 2 days and a three-day power factor of 4.9%. These results are inferior to the results obtained when a 30- minute contact time was used.

W p f, EXAMPLE VII 7 V Oil was treated by the same procedure as in Example V except that the mixture ot oil, sulfuric acid, copper, and ferric sulfate was held at 110 F. for 75 minutesin stead of 30 minutes. Thefinished oil had a Doble'life' without any initial treatment. This was done for cornpnrison purposes, and'is equivalent to'an initial treatment with sulfuric acid, copper, and ferric sulfate for atirne of zero minutes. The finished oil had a Doble life of 2 days and athree-day power factor of 30.0%.

V The resultsofrthe above experiments are summarized in Table I below.. V

Table I I '-'InitialTreating 'Trcat-- Percent Agents (All exingg Doblc Three- Example amplcscmployed Time Lite Day a clay finishing) min.. Pow-0r Factor Sulfuric acid. 30 2 18. 1- Sulfuric acid au 1 copper I 30 3 5.0 metal. V Sulfuric acid and ferric 2 7.0

sulfate. Sulfuric acid, copper metal 7 3O 3 5.0' and ferrous sulfate. 3 Sulfuric acid, copper metal, 7 30 3 1. 4

and ferric sulfate. 7 X 45 3 4.9

The-summary presented in Table I shows the superior results obtained by using the acid, copper metal, and ferric'sulfate treating agents for 30'minutes. Substantiall'y the same results' are obtained when the copper is replaced iby an-iuorganic copper salt. Likewise, ferric sulfate can be replaced by other inorganic ferric salts. In addition, the Contact time can beireduced to 20 minuteswithout any significant change in either the' Doble' 1 life or the three-day'power factor.

oil, 1

' We claim:

i 1. Method of treating rnin'eral oil' comprising the steps of concurrently contacting ai mineral oil inliquid phase with- (1)1540 lbs. ofconcentrated sulfuric acid per barrelof oil, (*2) at least 0.4% as'iron, basedcn weight of oil, of an inorganic ferric;salt, and (3)at least 1.5%,

(as copper, based on'weight of oil, of a compound selected from the'grou'p; consisting of copper metal and inorganic copper salts; saidfconcurrentcontacting being at a temf perature inthe range of'90 to F. and for a period of time in the 'rangeof20 -35 minutes, separating an'acid said treated'oilphase with adsorptive clay, I

2. Method of. claim-.1 in which the amount of ferric .phase from; a treated oil phase, and thereafter contacting JsaltisO.,41;0%, as'iron, based.,on' weightiof"oil. 3.1 Method of claim 1 in which the amount ofsaid PQUIJ QlS L -3.0%, as copper, based on weight of V 4. Method of claim 1 in which the time period is approximately 30 minutes.

5. Method of claim 1 in which the ferric salt is ferric sulfate.

6. Method of claim 1 in which the compound is copper metal.

7. Method of claim 1 in which the amount of adsorptive clay is 2540 lbs. per barrel of oil.

8. Method of treating mineral oil comprising the steps of concurrently contacting a mineral oil with (l) 0.41.0%, as iron, based on weight of oil, of an inorganic ferric salt, (2) 1.83.0%, as copper, based on weight of oil, of a compound selected from the group consisting of copper metal and inorganic copper salts, and (3) -30 lbs. sulfuric acid per barrel of oil, said contacting being at a temperature in the range of 90 to 130 F. and for a period of to 35 minutes, separating an acid phase from a treated oil phase, contacting said treated oil phase with -40 lbs. of clay per barrel of treated oil phase, and separating said adsorptive clay, whereby a refined oil is obtained.

9. Method of claim 8 in which the compound is copper metal.

10. .Method of claim 8 in which the ferric salt is ferric sulfate.

11. Method of claim 8 in which the period is approximately minutes.

References Cited in the file of this patent UNITED STATES PATENTS 1,920,248 Day Aug. 1, 1933 1,973,500 Morrell Sept. 11, 1934 FOREIGN PATENTS 7,005 Australia Nov. 24, 1932 

1. METHOD OF TREATING MINERAL OIL COMPRISING THE STEPS OF CONCURRENTLY CONTACTING A MINERAL OIL IN LIQUID PHASE WITH (1) 15-30 LBS. OF CONCENTRATED SULFURIC ACID PER BARREL OF OIL, (2) AT LEAST 0.4%, AS IRON, BASED ON WEIGHT OF OIL, OF AN INORGANIC FERRIC SALT, AND (3) AT LEAST 1.5%, AS COPPER, BASED ON WEIGHT OF OIL, OF A COMPOUND SELECTED FROM THE GROUP CONSISTING OF COPPER METAL AND INORGANIC COPPER SALTS; SAID CONCURRENT CONTACTING BEING AT A TEMPERATURE IN THE RANGE OF 90* TO 130*F. AND FOR A PERIOD OF TIME IN THE RANGE OF 20-34 MINUTES, SEPARATING AN ACID PHASE FROM A TREATED OIL PHASE, AND THEREAFTER CONTACTING SAID TREATED OIL PHASE WITH ADSORPTIVE CLAY. 